1. Field of the Invention
This invention relates to a safety restraint sensor system having a Hall element for determining whether a buckle is in a latched position with respect to a latch.
2. Discussion of Related Art
Conventional safety restraints, such as seat belts, use sensors which are activated when a buckle is inserted into a housing of the safety restraint assembly, in order to detect whether the buckle is securely latched. Conventional safety restraint assemblies also use magnets and magnetic flux sensors to detect whether the buckle is securely latched.
Sasaki, U.S. Pat. No. 4,943,087 discloses a conventional seat buckle assembly with a magnetic flux sensor to detect whether a buckle is within a housing of the seat buckle assembly. A magnet mounted on the buckle and a magnetic flux sensor arranged between an anchor base member and an emergency release buckle of the housing shield the magnetic flux sensor from detecting magnetic flux other than the magnet flux of the magnet. The magnetic flux sensor detects magnetic flux from the magnet mounted on the buckle and thus the presence of the buckle. When the buckle and the magnet are moved near the magnetic flux sensor, the magnetic flux sensor activates upon detection of the magnetic flux from the magnet. The magnetic flux sensor may be a Hall element.
Because the magnetic flux sensor taught by the '087 patent detects a presence of the buckle by sensing magnetic flux, any other magnetic flux can cause the magnetic flux sensor to detect a false positive latch condition. A false positive latch condition occurs when a sensor, such as the magnetic flux sensor, detects the presence of a buckle within a housing or latch and the buckle is either not within the housing, or the buckle is not fully latched within the housing. Because the magnet is mounted on the buckle for the magnetic flux sensor to detect the presence of the buckle, and because the buckle is constructed of ferrous material, the manufacturing process of the sensor of the '087 patent is relatively complex.
Saito, U.S. Pat. No. 5,218,744 teaches a magnet and a magnet holder molded or encased around the magnet. The magnet and the magnet holder are mounted on a buckle for use with a conventional seat buckle assembly which has a magnetic flux sensor. The magnetic flux sensor detects a presence of the buckle within a housing of the seat buckle assembly when the magnet and the buckle are positioned near the magnetic flux sensor. The magnetic flux sensor of the '744 patent may also detect a false positive latch condition. Because the magnet taught by the '744 patent is attached to the buckle, the manufacturing process for positioning and then constructing the buckle is also relatively complex.
Yamamoto et al., U.S. Pat. No. 4,920,620 teaches a mechanical sensor for detecting whether a buckle is inserted within a housing of a seatbelt buckle assembly. The mechanical sensor moves from a disengaged position to an engaged position when the buckle is inserted within the housing and locked with a latch piece. The seat buckle assembly of the '620 patent purportedly prevents a false latch condition, because the mechanical sensor does not move from the disengaged position until the buckle is engaged in the housing. The mechanical sensor taught by the '620 patent has more moving or wearing parts than the magnetic flux sensor, thus the mechanical sensor is more likely to fail.
Hall Effect Transducers--How To Apply Them As Sensors, Honeywell, MICRO SWITCH Division, 1982, (the Honeywell reference) teaches how to combine a Hall element with a magnet to create a Hall sensor which can detect a magnetic field and, as a result, the presence or absence of a vane. The Hall element is positioned near the magnet and activated by a magnetic flux. When a vane is introduced between the Hall element and the magnet, the magnetic flux is shunted in a direction parallel to the vane, and the Hall sensor is electronically placed in an OFF state. The arrangement of the Hall element, the magnet, and the vane is called a vane operated position sensor, or a vane sensor.
Conventional sensors for safety restraints have several shortcomings. For example, in many conventional seat buckle assemblies a magnet is mounted on a buckle constructed of a ferrous material. The magnetic attraction between the magnet and the buckle makes it difficult to handle the magnet during assembly and thus complicates the manufacturing process.
Conventional sensors for safety restraints are also prone to developing false latch conditions. Conventional safety restraints may indicate a false latched position when the buckle is inserted but the latch is not fully engaged. Conversely, a conventional safety restraint may indicate a latched position when the latch is fully engaged but the buckle is not fully inserted. Many conventional sensors attempt to eliminate the false positive latch condition by using a mechanical sensor instead of a magnetic sensor. Mechanical sensors have more moving parts and thus are predictably less reliable than magnetic sensors.
There is an apparent need for an inexpensive, easily manufactured safety restraint sensor system having a latch position sensor. There is also an apparent need for a safety restraint sensor system having the capability to detect that both a buckle and a latch are in a latched position and/or an unlatched position.